Performing CT scans of body extremities such as arms, hands, legs and feet presents special difficulties. This is especially true in the veterinary context where the patient is a horse. Specifically, it has proven especially difficult to perform good CT scans of a horse's leg for a number of different reasons, including at least the following.
First, the geometry of a standing horse is extremely difficult to work with. Specifically, the separation distance between a standing horse's legs can be as little as 4 inches apart. In addition, the image of the leg and foot should be taken under natural loading during a natural standing pose. This provides little room for a veterinarian to safely maneuver X-ray equipment around the horse's legs. In addition, a typical exam for a performance horse can require 52 separate projection images taken for each of the 4 legs. Performing such an exam quickly is very difficult.
Second, traditional CT systems use only one X-ray source and a flat panel detector and must therefore acquire image data over multiple rotations to cover the entire volume of the leg or other object being imaged. Unfortunately, the X-ray source-to-detector distance must be increased to minimize the number of rotations required. This is difficult to achieve in tight geometries. Moreover, to fully illuminate the height of the detector, a significant source-to-image distance is required so that a standard cone-beam X-ray beam can expand enough to cover the rotating detector. Once again, it is difficult to work within such geometric constraints. It can also be unsafe both for the veterinarian and for the horse.
Third, despite taking a large number of images, important pathology such as stress fractures and micro-fractures can still be missed in a CT scan. To visualize such fractures, it is necessary to acquire the image with the source and detector lined up such that the crack or fracture in the bone is seen along its axis (i.e.: by lining up the seam of the crack with the X-ray beam).
Fourth, in conventional CT systems, the object to be imaged is typically placed equidistant between the source and the detector, and the source and detector are rotated around the object. This geometry is simply not possible to use with a standing horse's legs.
In short, traditional CT scanners that image whole-bodies are expensive to own and operate (especially if they image whole-bodies), and their geometries and rotational paths are completely unsuited to work with long narrow objects that are positioned close together (for example, the legs of a standing horse). Recently developed cone-beams systems have the advantage of acquiring images quickly with less expensive imaging components but have the disadvantage of being very large due to the need to rotate a flat-panel detector. Moreover, since the cone-shaped beam of the X-ray expands outwards towards the detector, the proximal side of the object being imaged will have a smaller region of exposure than the distal side. Lastly, requiring multiple rotations of the equipment increases the time to acquire the full image.
What is instead therefore desired is a system that would rapidly image a horse's leg (or any other object) in a fast period of time and within a small area of working space. As will be explained below, the present system provides solutions to these problems.